Reflections on the Interpretation of Heavy Mineral Analyses

Abstract

ABSTRACT The study of heavy minerals, an important field of endeavor for the sedimentary petrographer prior to 1940, has declined in recent years. This decline, caused primarily by the disappointing results of heavy mineral correlation, is regrettable because in regional stratigraphic and paleogeographic research the method is capable of contributing important information concerning the location and character of source areas and the distribution patterns of sediments. The following factors can modify the heavy mineral composition and limit the interpretation of the assemblage in terms of source area conditions: (1) weathering, (2) abrasion, (3) selective sorting, and (4) post-depositional solution. This paper attempts to show that (3) and (4) are of minor importance. In basins with a low rate f sediment supply and under conditions of intense weathering and reworking the others can strongly modify the composition of the heavy mineral assemblage. In basins of rapid deposition deriving their sediment in general from source areas with active erosion, the influence of all factors is negligible and the heavy mineral assemblage directly reflects the petrography of the source area. An example illustrates the type of problem for which heavy mineral analysis is of value. Problems of sediment source and distribution in the Mississippi valley and the Gulf Coastal Plain in the Cenzoic are a field where heavy mineral analysis is considered rewarding.